Microsoft Corp. and Yammer Inc. today announced that they have entered into a definitive agreement under which Microsoft will acquire Yammer, a leading provider of enterprise social networks, for $1.2 billion in cash. Yammer will join the Microsoft Office Division, led by division President Kurt DelBene, and the team will continue to report to current CEO David Sacks.

"The acquisition of Yammer underscores our commitment to deliver technology that businesses need and people love," said Steve Ballmer, CEO, Microsoft. "Yammer adds a best-in-class enterprise social networking service to Microsoft's growing portfolio of complementary cloud services."

Launched in 2008, Yammer now has more than 5 million corporate users, including employees at 85 percent of the Fortune 500. The service allows employees to join a secure, private social network for free and then makes it easy for companies to convert a grassroots movement into companywide strategic initiative.

"When we started Yammer four years ago, we set out to do something big," Sacks said. "We had a vision for how social networking could change the way we work. Joining Microsoft will accelerate that vision and give us access to the technologies, expertise and resources we'll need to scale and innovate."

The acquisition is subject to customary closing conditions, including regulatory approval.